This invention concerns a contactor of the type which includes a magnetic system defined by a coil and a core of which the core is movable to selectively move a contact bridge holder and contacts carried thereby between open and closed positions for selectively opening and closing an electric circuit. Typically such contactors include conventional thermal trippers and magnetic trippers for each electrical phase and an appropriate actuator system for controlling the opening and closing of the contacts.
Various designs of contactors and motor protective switches are conventional, and ordinarily a motor protecting switch includes a contactor associated with a separate thermal protecting device (tripper) mounted in a separate housing. The system of contacts and the magnetic system driving the system of contacts are mounted in a single housing which is located either on the assembly side of the system of contacts or on the side of the system opposite (generally above) the assembly side. The conventional core of the magnetic system is connected to a contact bridge holder which carries contacts movable with the bridge holder between opened and closed positions of associated fixed contacts.
In another design a thermal tripper is present in the housing to operate or trip when the current or thermal load of a motor or the like exceeds a certain value. However, in spite of elaborate designs of such conventional contactors the thermal tripper operates unacceptably because the current (the thermal load) as a general rule increases very slowly. Obviously, because of such slow reaction it is difficult to protect an electrically motor against rapid current increases, and in most contactors of this type a separate safety mechanism is required and such mechanism is normally mounted in the separate housing outside of the contactor housing. Because of the latter, on the whole eighteen different connections are required between the various electrical terminals of such conventional contactors.
A lesser number of connections (twelve connections) are known in another conventional contactor which includes a magnetic system and a system of contacts which are connected through electrical conductors to a separate motor protecting switch. However, even twelve separate connections is unacceptable because the wiring of the contactor is complex, time consuming, and both manufacture and installation are expensive because of the added expenditure of money for materials for the many connectors of these conventional contactors. Aside from the cost involved, these conventional contactors also require a considerable amount of installation space, as when installed relative to a switching console.
In yet another known contactor, much of the wiring thereof is carried out largely within the contactor and the contactor is of a relatively compact design. This contactor includes thermal trippers for the three electrical phases and quick short trippers or magnetic trippers which drive a switch latch which through a system of contacts will open a motor protecting switch. An undervoltage or power tripper may also be provided. However, this contactor includes the drawback that switching between ON and OFF positions can only be carried out manually by actuating an associated ON/OFF button, except for the automatic shut off by the motor protecting switch.
There is a substantial demand for a contactor which can be automatically turned ON and OFF. Moreover, there is a need for turning the contactor ON and OFF by either than the manual or magnetic operation of the contact bridge holder and doing so by implementation from another suitable location. For instance, when the contactor is integrated into a switching console together with many other switches, it is desirable to operate the contactor between the ON and OFF positions manually or automatically from other than the conventional side heretofore provided, illustratively from a machine-tool that includes the to-be-protected electric motor.
Another relatively compact contactor is known which reduces wiring through a system of contacts and actuating means thereabove in one housing near the assembly side with the thermal and magnetic trippers for each electrical phase mounted on an adjacent side of the actuation means and cooperative therewith. On the other side of the actuation means there is a drive for the electromagnet with the armature thereof joined through knuckle joints to an extension of a common contact bridge holder of a system of contacts. Moreover, a slider is provided in this contactor which is engaged by the knuckle joints and by associated thermal and magnetic trippers.
In all of the foregoing conventional contactor designs there is explicit or implicit therein the assumption that upon overloading and tripping the contacts of the system of contacts actually do open every time. However, this is not often times the case. As regards contactors equipped with thermal and magnetic trippers, these trippers driven by actuation means act solely on the conventional system of contacts. Because of the great many switching steps carried out by such system of contacts and associate arcing and mechanical wear and metal fatigue, contact-welding can take place in an unforeseeable manner and time, whereby the ultimate desire for optimal reliability of switching is not obtained.